1. Technical Field
The invention relates generally to the field of vision improvement and more specifically concerns a method for providing an spectacle ophthalmic lens by calculating or selecting a design. The spectacle ophthalmic lens can be, e.g., a progressive lens, a unifocal lens. The invention also concerns a method for making a spectacle ophthalmic lens. Furthermore, the invention concerns a piece of software set up for implementing the calculation method for the design of a spectacle ophthalmic lens of the invention.
2. Description of the Related Art
Spectacle ophthalmic lenses are worn and widely used for correcting many different types of vision deficiencies. These include defects such as near-sightedness (myopia) and far-sightedness (hypermetropia), astigmatism, and defects in near-range vision usually associated with aging (presbyopia).
Ophthalmologists or optometrists routinely improve the visual acuity by correcting refractive errors in terms of sphere, cylinder and axis. Said refractive errors are low order aberrations.
Astigmatism is a geometrical aberration converting the image of a point into two perpendicular straight lines (sagittal and tangential focals). The distance between these two straight lines represents the astigmatism value of the optical system, and their orientation is the astigmatism axis.
Astigmatism occurs when the refractive error in an eye is meridian-dependent. This is usually due to one or more refractive surfaces, most commonly the anterior cornea, having a toroidal shape. The astigmatic refractive error is a second-order aberration.
The astigmatism of an optical system is due both to locally toric surfaces and to the oblique character of rays (when image and object are beyond the axis). Complex surface such as in progressive lens are generating astigmatism aberration that varies at each point of the lens. The difference between the astigmatism of the lens and the prescribed astigmatism corresponding to the refractive error of the eye is called the residual astigmatism.
Document WO2009/043941 discloses a method for providing a spectacle ophthalmic lens to a wearer comprising the step of measuring high order aberrations (HOA) of an eye and calculating or selecting the said spectacle ophthalmic lens design based on the HOA measurement.